Answer Posted / varun rekhi

Onload Tap Changer (OLTC) is used with higher capacity
transformers where HT side voltage variation is frequent
and a nearly constant LT is required. OLTC is fitted with
the transformer itself. Multiple tappings from HV windings
are brought to the OLTC chamber and conacted to fixed
contacts. Moving contacts rotates with the help of rotating
mechanism having a spindle. This spindle can be rotated
manually as well as electrically with a motor. Motor is
connected in such a way that it can rotate in both the
directions so as to rotate the OLTC contacts in clockwise
and anticlock-wise direction. Two push buttons are fitted
on the LCP (local control panel) to rotate the motor and
hence the OLTC contacts in clockwise and anti-clockwise
direction. This movement of contacts thus controls the
output LV voltage of the transformer. So rotating of OLTC
contacts with spindle or push buttons in this way is a
manuall process. In case this process of rotating the OLTC
contacts and hence controlling the LV side voltage is to be
done automatically then a RTCC (Remote Tap Changer
Controller) is installed with the transformer HT Panel. The
RTCC sends signals to LCP and LCP in turn rotates the motor
as per the signals received from the the RTCC


OLTC(on load tap changer)is a mechanism used in transformer
for changing the tapping position on primary side(HV)of
transformer.For any installation mostly in industrial areas
and rural areas the voltage on HV of the transformer will
not be 11kv(taking an example of 11kv System)and
correspondingly the output will not be 433v.To maintain a
constant 11kv/433v the tap changer on the Primary/HV side
of the transformer is either raised or lowered to maintain
constant 11kv input to transformer.Normally it is raised or
lowered in steps of 2.5% of normal KV value.

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